The invention relates to a method for producing optical polymer components having integrated fibre-chip coupling using casting technology, wherein the optical polymer components have a region for accommodating an optical waveguide and a V-shaped positioning trench for accommodating an optical fibre to be coupled to the optical waveguide. More particularly the present invention relates to such a method which is applied in the mass production of monomode or multimode components in integrated optics having monolithically integrated fibre-chip coupling.
The increasing use of integrated optical components for optical communications, for sensory analysis and the field of computers (optical databus) lends optical interconnection technology (chip-fibre coupling) an ever growing significance. In this case, even relatively small private exchanges having approximately 1,000 subscriber lines require, for example several thousand optical connections between the individual switching substages, since the number and complexity of the integrated optical components on individual substrates is severely restricted owing to the extreme aspect ratios in optics.
In such applications, the realisability and reliability (mechanical and thermal stability) of optical interconnection technology determines and the required outlay on connections finally determine the achievable degree of expansion of an optical exchange system or of an optical communication network.
The light coupling efficiency in the case of coupling of glass fibres and integrated waveguides of the components depends strongly on the spacing of the end faces and very strongly on a lateral displacement as well as on an angular tilt of the optical axes with respect to one another. Consequently, in the coupling the glass fibre has five degrees of freedom which have to be optimised independently of one another: one axial degree of freedom, two lateral degrees of freedom and two angular degrees of freedom. In the case of the field distributions typical of glass fibres, a lateral offset of only a few .mu.m, for example, already leads to coupling losses in the dB range. An effective coupling method requires a reduction in the degrees of freedom as well as a possibility of simultaneously positioning all the fibres of a bundle. Appl. Opt. (1978), page 895, "Optical coupling from fibres to channel waveguides formed on silicon", J. T. Boyd and S. Sriram discloses etching V-grooves into a silicon substrate as positioning trenches for the glass fibres. The anisotropically etched V-grooves are bounded on all sides by slowly etching {111}--planes which enclose an angle of 54.7.degree. with respect to the wafer surface. Arranged flush with these V-grooves are the integrated waveguides, it being possible to optimize the width of the grooves such that the resulting shape of the groove causes the fibre core to lie in the same horizontal plane as the optical waveguide. The end face of the V-groove situated in the region of the coupling surface to the optical waveguide is likewise inclined at an angle of 54.7.degree., so that the glass fibre cannot be pushed up completely as far as the waveguide. Boyd and Sriram propose as a solution to this problem to provide the glass fibre with an end face inclined likewise at 54.7.degree. in order in this way to push the fibre core against the integrated optical waveguide as far as butt coupling. However, this method has the disadvantage that a complicated processing of the end face of the fibre is required, and the fibre may be inserted into the groove only in a specific position. Moreover, in the coupling there is the risk of the two end faces sliding on one another, or of at least the end region of the fibre therefore being pushed out of the groove. An additional difficulty arises from the necessity of providing not only the fibre, but also the integrated waveguide with a correspondingly inclined end face.
This method has, furthermore, the decisive disadvantage that mass production of integrated optical components is impossible. However, it is precisely mass production that is a precondition for efficient and practicable application.
H. Hosokawa et al. disclose in Integrated Photonics Research Conf., Paper MF6 (1991) carrying out the simultaneous production of optical waveguide structures and grid structures for light coupling by means of a compression technology and subsequent photopolymerisation. However, this compression technology for monomode optical waveguides is not capable of realising the guidance of fibres integrated on a substrate.
Also known, moreover, is the principle of casting by electroplating and injection-moulded duplication of microstructures by lithography using synchrotron radiation, the so-called LIGA method. Here, the primary structures to be cast are usually produced by X-ray exposure of plastics on the synchrotron and the mould inserts for the injection moulding are prepared therefrom by electroplating. It is not possible using this method to achieve an exact height adjustment of fibre-guiding structures with the simultaneous production of optical waveguides and fibre-guiding structures. However, as also described above, it is precisely the exact adjustment that is the indispensable precondition for achieving high coupling efficiencies between fibres and waveguides, since even the slightest vertical and/or lateral deviations in the submicrometer range lead to impairment of efficiency.
Furthermore, it is disadvantageous in all known methods that no final adjustment of the fibre-chip coupling is possible by means of a protective covering which simultaneously protects against mechanical and other external influences.